Dynamic field modelling of torque and radial forces in vector-controlled induction machines with bearing relief

The paper addresses the bearingless induction motor based on the concept of dual-pole windings, one controlling the motor torque and the other the generated radial forces. Such machines have been investigated experimentally in the past. The paper presents a simulation model capable of investigating the effect of induction-machine design on the generation and control of the radial force. The simulation is based on the dynamic reluctance-mesh field model embedded in vector control systems for the decoupled control of torque, flux and radial force. In the paper, the rotor is constrained by a mechanical bearing so that the radial force is used to cancel the rotor weight to effect ‘bearing relief’. The paper summarises the modelling method, investigates the radial force production in both cage and wound rotor machines, and introduces a mixed field orientation method for the decoupled control of the torque and radial forces. Simulations are undertaken showing good generation of radial force under zero speed, acceleration and transient load conditions.